To date, a variety of driving devices that use piezoelectric elements have been proposed as driving devices for causing a lens or the like to move. In below-listed Patent Document 1, a driving member is used that is displaced in an axial direction on the basis of an expansion/contraction operation of a piezoelectric body. A member that is to be driven can be moved by being engaged with this driving member through a frictional force. In Patent Document 1, the to-be-driven member is pitch fed in the axial direction by repeatedly performing an operation in which driving is performed by applying a voltage to the piezoelectric body in a direction that is the same as the polarization direction of the piezoelectric body and an operation in which driving is performed by applying a voltage in the opposite direction.
On the other hand, in below-listed Patent Document 2, an ultrasonic motor is disclosed that utilizes flexural vibration and another kind of vibration. Here, a configuration is adopted in which a cylindrical slider is inserted into a through hole of a disk-shaped substrate and the slider moves in an axial direction thereof. Piezoelectric elements are provided on both surfaces of the disk-shaped substrate and composite resonance made up of flexural vibration and radial-direction vibration of the disk is generated in the substrate.
Patent Document 1: Japanese Patent No. 4492756.
Patent Document 2: Japanese Unexamined Patent Application Publication No. 1-298968.
In the driving device described in Patent Document 1, the movable body is unable to satisfactorily follow the axial expansion and contraction of the driving member. Consequently, the movable body cannot be pitch fed with certainty. In addition, the movable body sometimes moves backward in a forward movement period. Therefore, it is difficult to make the movement speed of the movable body high and the movement speed is unstable.
On the other hand, in Patent Document 2, composite resonance made up flexural vibration and radial-direction vibration is utilized. In this case, it is not easy to generate flexural vibration and radial-direction expansion-contraction vibration with the same period. Consequently, it is difficult to pitch feed the movable body and it is also difficult to stabilize the movement speed of the movable body.